1. FIELD OF THE INVENTION
This invention relates to improvements in check valves, such as those suitable for use with high velocity, high pressure fluid systems, and more particularly, to such valve assemblies having a valve closure element exhibiting improved operating characteristics and fluid dynamic response.
2. DESCRIPTION OF THE PRIOR ART
Various types of check valves, butterfly valves and the like, have long been well known and are used in many diversified applications. For these different applications, the valve assemblies range from those which are extremely small and made of lightweight material, such as plastic and aluminum, to those which are quite massive in size and are made of cast metal. While such larger valve assemblies are inherently more difficult to handle, both large and small check valves exhibit certain common characteristics and have certain desirable features the attainment of which has presented serious problems to the valve engineer, as well as the ultimate user.
For example, valve assemblies heretofore available have typically exhibited characteristics such that the valve closure members thereof tend to oscillate and, in certain cases, cause rapid deterioration and failure in operation. Also, check valves of the prior art have failed to recognize the fluid dynamics involved in a valving operation and often seriously impede fluid flow even in the desired direction. While early attempts to remedy some of these deficiencies as well as many others have resulted in improved valve designs, a check valve assembly having a design which takes into consideration the dynamics of fluid flowing therethrough and has a natural tendency to resist oscillation has heretofore been unavailable.
In considering the prior art, it may be illustrative to briefly trace the history of the development of the modern check valve. Initially, it was felt that the easiest way to produce a check valve would be to provide a flat, annular seat whose axis coincides with that of a flow path, such as that within a pipe, and to additionally provide a circular flat plate for cooperation with the flat seat. The flat plate closure member was then typically journaled for rotation about an axis normal to the axis of the valve seat and placed outside the flow path, typically on or about the periphery of the seat. In this manner, forward flow would force the flat plate to open away from the annular seat and reverse flow would cause the plate to firmly engage the seat thereby closing the valve.
While the foregoing valve arrangement was believed to be a satisfactory solution, it was soon recognized that the same exhibited a serious disadvantageous characteristic, namely, under steady flow conditions the valve tended to oscillate causing severe damage to the valve seat during operation. Of course, it should be further appreciated that this oscillation of the valve plate often had destructive consequences especially in cases where the valve closure member itself had a three or four foot diameter and weighed approximately 1000 pounds. The natural solution to this problem was to equip the valve assembly with an appropriate damping mechanism; however, this obviously increased the cost and complexity of the overall system and treated the symptoms rather than the problem.
The valve engineer, in attempting to overcome the problems outlined above, moved to a second generation check valve of the type exemplified by U.S. Pat. No. 1,744,798. This type of valve arrangement moved the axis of rotation of the valve member from its position adjacent or outside the periphery of the valve seat to a position within the valve seat but slightly offset from the valve center line. This, of course, had an affect in reducing the high torque required to maintain the valve closure member in a fully open position, but nevertheless failed to eliminate the oscillation problem exhibited by previously available devices. Moreover, the oscillation problem became even more critical since the second generation check valves had a frusto-conical seat designed to provide a direct metal-to-metal contact with a conforming frusto-conical edge of the closure member. This arrangement requires that critical tolerances be maintained, and such tolerances are incapable of being continuously met under conditions where oscillation of the valve exists. Again, it became necessary to equip these valves with damping arrangements in order to reduce the oscillations and maintain the valves in proper working condition.
While the foregoing development of check valves resulted in certain improvements, it failed to provide a fully satisfactory assembly which eliminated the need for an associated damping mechanism. This is due primarily to the fact that prior to the present invention, the check valve designs of the prior art did not take into consideration the fluid dynamics which exist in a situation requiring the provision of a check valve and, in fact, exhibited the reverse characteristics to those normally desired. In other words, when the valve is closed, a high pressure differential exists across the closure member while no flow occurs; on the other hand, with the valve open, no pressure differential exists while a high flow situation is established. Thus, the fluid pressure available to perform work is maximum when the valve is closed and decreases to a minimum when the valve is fully opened. The prior art valve exhibited characteristics such that the torque required to initially open the same was small and increased to a rather large value. It can therefore be appreciated that the fluid pressure was at its minimum point when the prior art valves necessitated that the maximum torque be exerted. The present invention has thus recognized the essential or basic problem which has plagued the prior art in producing valves which oscillate in operation, and has provided an effective solution to the problem in the form of a valve design in which the torque necessary to open the valve decreases, rather than increases, as the same opens from its closed position.